The construction and operation principles of a continuously operating double-shaft screw-type extruder and its use in the preparation and production of virtually all types of plastic materials is well known in practice and disclosed in literature, see for example, "Kunststoffmaschinenfuhrer" [Guide to Machines for Plastics], pages 960 to 968, Carl Hauser Verlag, Munich and Vienna, 2nd Edition, '84.
In this regard, such screw-type extruders are known which have at least one feed unit and one or more degassing apertures and, optionally, a granulating unit.
In this case, the addition of the starting materials and additives to the extruder can be effected by a gravity system through vertical supply ducts or by means of a vertical or horizontal drive unit.
A batch-type mixer is disclosed in DE-OS 21 29 468 and its US equivalent, U.S. Pat. No. 3,717,330 consisting of a funnel-shaped container in which two screw-type helices are installed, which can be driven from below and mutually scrape against each other and against the inner surface of the wall of the container. The mixer is used for the final processing stage in condensation-type polymerization reactions.
In this way, in essence, a batch-type final processing procedure takes place. However, this self-cleaning mixer is not suitable for the intensive processing of the plastic compositions in order to achieve high quality final products since adequate pressure can only be developed in the lower regions of the container while in the upper regions of the container, dead spaces are produced where intensive mixing does not take place.
In order to increase degassing efficiency, it is also known to install a separate primary stage before the screw-type extruder which consists of a flash evaporator together with a double-shaft screw-type supply unit by which multi-step degassing of polymer solutions, which contain a high proportion of solvent, is effected. High capital expenditure for the equipment is necessary in this case.